Horn for X15

I've decided on the BM-D740 (or maybe 50) for my X15s but I've just realised I'm restricted somewhat as to which horns I can fit on to it.  I don't really want to start modifying the design so it leaves me with a maximum area of 240mm x 480mm.  This rules out the 18sound horns I've been considering and the B&C ME90.
 
I don't want to use the PH-3223 because of the rapid changes in flare angle it has (along with quite a few other P.Audio horns) and the apparent "horn honk" this can cause, as described here:
 
http://www.audioheritage.org/vbulletin/showthread.php?t=12967
(scroll down to "Horn distortion due to internal reflections: “Horn-Honk”")
 
... I was about to write a list of horns I'm considering but those criteria have ruled out any I can find!  If anyone has any other suggestions please let me know.
 
In summary:
 
1.4/2" throat
No rapid changes in flare angle, inc. mouth termination if possible... i.e. curved
60x90 coverage or thereabouts, will settle for 60x40
No bigger than 240mm x 480mm

Thanks
Phil


Edited by Phil.2008 - 02 February 2009 at 5:55pm

Thing that puts me off is having to construct the shelf/port-depth thing.  Still I might have a go - hadn't considered moving the horn so that might be an idea.  Nice pics btw

I've been playing around with the port positioning and I've come up with this:


This is done to scale in Autocad.  Basically each triangle has half the area of one of the original two ports, the idea being that I'll just put a little shelf going back the same distance as in the orignal design behind each one (112mm).  Firstly, would that work... does the number of ports make any difference or is it the total area that matters? i.e. if you only wanted an 18mm port depth could you just drill the right amount of holes the right width in it?

That's the B&C ME90 in there by the way, the XT1464 was only just too high.

I've had a go at modelling the original X15 in WinISD, but I'm not sure about the numbers it's giving me.  Firstly, are these params right for the driver:


I've set the rest of the values up as follows:

Driver
-------
Number of drivers: 1
Normal

Box
-----
Vented
Volume: 100 litres
Tuning freq: 50 Hz

Vents
-------
Number: 2
Shape: rectangular
Vent diameter: 0.231 x 0.060 metres
Vent length: 0.220m
Vent mach: 0.03

Now, the vents on the original design are 130mm deep, so what's going on here?  have I put some values in wrong... is WinISD giving a different number than Rog might have come up with via other means... or is the fact that the box is a trapezoid shape somehow taken in to account in Rog's calculations (something I thought of afterwards) which of course means that the apeture inside the box is smaller than that of the baffle.

Re. my new design, I want to keep the same box volume because I want to be able to use them as full-range speakers... is that right? i.e. does the volume affect the low-end response?

There are so many questions and variables going round in my head it's hard to keep track of them!  I feel like I'm jumping in a the deep end and not knowing what's going on a bit... any answers / suggestions welcome!

Phil

Those traingle ports are OK for a square cab, think about doing the port duct though, even if you did just a bottom shelf and side shelf to the triangle, the port would taper in with the sides. Keep the ports away from the sides. Like this

Edited by nickyburnell - 04 February 2009 at 12:05am

It'd be a lot easier if I could make 18mm-deep ports like the X12.  I understand this could affect response at higher SPL's though?  What do people think?

This is the paragraph that I read about this (from http://www.hometheaterhifi.com/volume_5_2/cmilleressayporting.html):

In addition, the size of the port itself, regardless of tuning frequency, can have quite an effect. A small port, although it does not have to be very long, must move a lot of air through a very small opening. This make turbulence more of a difficult thing to cope with. But, it also makes for a more non-linear resistance to air movement. In other words, as output increases, the resistance to air flow increases, and the benefits of a port decrease, making the output look more like a leaky sealed system. The larger the port, the less it happens, but the characteristic is always there. Very large ports, say 4 inches wide, will be FAR more linear in this regard than a port, say 1 inch in diameter. However, as the surface area doubles, the required length doubles as well, so that a port 4 times wider in diameter, which has an opening 16 times greater in surface area, must be 16 times as long to maintain the same tuned frequency. On top of that, large ports may suffer from pipe resonance (like a pipe organ) which can be really annoying.


Edited by Phil.2008 - 04 February 2009 at 3:10pm

OK, how does this sound (from Win ISD):

2 Vents at 270mm x 30mm, 131mm port depth

Should give tuning frequency of 50Hz and maximum port air velocity of 1.5 (whatever unit that is) at 50Hz

And looks like this:


If someone could check the WinISD file I'd really appreciate it: www.philreeve.com/X15.wpr

By the way I'm planning on making ports parallel to the side wall so that they're the same area all the way down.

Looking at the diagram it might be nicer if I made them a bit wider horizontally and shorter vertically but have I got it basically right?

Thanks

Edit: updated WinISD file as I had the driver params wrong



Edited by Phil.2008 - 04 February 2009 at 5:53pm